This invention relates to underwater imaging systems, and more particularly to multi-camera, co-registered fields of view, underwater imaging systems for stationary or underwater vehicle applications.
Underwater operations are usually done by divers in shallow water, however, in deeper water or when hazardous conditions exist, it is common to use underwater vehicles. A remotely-operated vehicle (ROV), tethered to a surface vessel for operation by a human is the most widely used in commercial endeavors. Recently, for oceanographic and naval purposes, the unmanned, untethered, underwater vehicle (UUV) has been developed. In these vehicles, autonomous operation is required and the invention can play a key role in automated object identification.
Investigation of underwater wrecks, lost objects, pipelines, cables, unexploded ordnance, sea mines and other objects of interest can be a challenging problem depending on water clarity. In low or moderate turbidity water, optical cameras, particularly electro-optical cameras, can provide high-resolution images of such underwater objects. Water turbidity, however, can be a serious limitation to optical imaging, especially in littoral waters or when the sea floor is stirred up by the vehicle.
Acoustical cameras operating in the low MHz frequency range can image in very turbid water, producing 3D acoustical images, which may augment or substitute for the optical images. Other operations that could be undertaken by an ROV or UUV equipped with the invention include object recovery, connection to in-situ equipment, hull searches, and bottom surveys along piers or other mooring areas in addition to the U.S. Navy""s interest in mine neutralization.
Underwater imaging is a highly developed technology. There are optical methods such as conventional cameras with floodlights or strobe (flash) lighting, such as described in D. J. Harris, xe2x80x9cEyes Under the Seaxe2x80x9d in Underwater Imaging, Proc. SPIE, Vol. 980, pp. 53-56, 1988. There are range-gated, intensified, electro-optical cameras such as described in L. H. Gilligan et al, xe2x80x9cRange gated underwater viewingxe2x80x9d in Underwater Imaging, Proc. SPIE, Vol. 980, pp. 36-40, 1988. And there are laser lines scanners such as described in B. W. Coles, xe2x80x9cRecent Developments in Underwater Laser scanning Systemsxe2x80x9d in Underwater Imaging, Proc. SPIE, Vol. 980, pp. 42-52, 1988.
There are also acoustical methods such as described in E. O. Belcher et al, xe2x80x9cAcoustic, Near-video-quality Images for Work in Turbid Waterxe2x80x9d in Proc. Underwater Intervention 2000 Conference, Houston, Tex., January 2000, and acoustical cameras such as BAE SYSTEMS Acoustical Camera as described in T. E. White et al, xe2x80x9cImaging with an Underwater Acoustical Cameraxe2x80x9d, in Information Systems for Navy Divers and Autonomous Underwater Vehicles Operating in Very shallow Water and Surf Zone Regions, Proc. SPIE Vol. 3711, 1999.
The invention is an underwater, multi-mode, imaging and target recognition system with different imaging devices having overlapping fields of view so that the images from each device can be compared and combined for improved pattern recognition. Among the combination of imaging modes contemplated are an acoustical camera and a real-time, range-gated, intensified, electro-optical camera having substantially overlapping fields of view for co-registered imaging of underwater objects at close ranges. The system may be mounted in an unmanned underwater vehicle but may be used in other fixed or mobile configurations. The coupled fields of view may be steerable in an arc around at least one axis over a large field of regard with a servo-controlled rotating mirror system, while the vehicle or platform, and/or the target, is moving or hovering. An on board or remote computer capability with an automated target recognition capability may use the multi-modality images to provide enhanced target recognition and/or autonomous operation in unmanned missions.